This invention is directed to a method of forming and attaching thermally stable polycrystalline diamond (“TSP”) materials to form new cutting elements and bits incorporating such cutting elements, as well as to such cutting elements and bits.
A TSP material is typically formed by “leaching” at least a substantial portion of a catalyst, such as cobalt, from a polycrystalline diamond (“PCD”) material using a leaching agent. When formed, PCD comprises individual diamond crystals that are interconnected defining a diamond network. Catalyst particles, e.g., cobalt particles, are often found within the interstitial spaces in the diamond network. Cobalt has a significantly different coefficient of thermal expansion as compared to diamond, and as such, upon heating of the PCD, as for example upon frictional heating of the PCD which occurs when the PCD is used to cut earth formations, the cobalt expands, causing cracking to form in the network structure, resulting in the deterioration of the PCD layer. PCD having a second phase metal catalyst will generally not have thermal stability at temperatures above 700° C. By removing, i.e., by leaching, the catalyst (e.g., the cobalt) from the diamond network structure, the PCD layer becomes more heat resistant, as well as less prone to cracking when heated.
Typically, to form a PCD layer, a substrate of cemented tungsten carbide (a substrate where tungsten carbide particles are cemented together with a binder such as cobalt) is placed adjacent to a layer of diamond particles, which may also be premixed with a catalyst, such as cobalt, in a refractory metal enclosure typically referred to as a “can”, as for example a niobium can, and the combination is subjected to a high temperature at a high pressure where diamond is thermodynamically stable. This process is referred to as a high-temperature-high-pressure sintering process (an “HTHP sintering process”). This process results in the recrystallization and formation of a PCD ultra hard material layer bonded on the tungsten carbide substrate. The PCD layer is then removed from the substrate by cutting off and by lapping off the substrate, as necessary. The removed PCD layer is then leached to substantially remove all of the catalyst to form the TSP material layer. Typically at least 95%, and in many cases over 98% and even over 99% of the catalyst is removed. Removal of the catalyst frees the interstitial spaces in the diamond network, i.e., it creates voids in the diamond network. The TSP material layer may then be attached to another substrate by brazing, or by a high-temperature-high-pressure process (an “HTHP bonding process”) where a cemented tungsten carbide (WC-Co) substrate is provided adjacent the TSP material layer and is heated at a sufficient temperature to melt and get infiltration of a binder, such as the cobalt in the tungsten carbide, to infiltrate the TSP material layer and at a sufficient pressure for attaching the TSP material to the substrate forming a TSP material cutting element, such as a TSP material cutter or compact. Moreover, an infiltrant such as a metal or metal alloy infiltrant, as for example copper, silver, copper alloys and silver alloys, which have a melting temperature that is lower than the melting temperature of the diamond particles, may also be used to infiltrate the TSP material when being attached to the substrate. The infiltrant infiltrates into the voids created by the leaching process attaching the TSP material to the substrate. It should be noted that an HTHP bonding process is not a sintering process as is the HTHP sintering process referred in the formation on the PCD. Moreover, the times, temperatures and/or pressures in an HTHP bonding process may be different than those in an HTHP sintering process. In addition, a sintering process requires a catalyst, whereas the bonding process requires an infiltrant. For convenience the term “HTHP process” is used herein to refer to a process requiring high temperature and high pressure as for example an HTHP sintering process or an HTHP bonding process. It should be noted that the acronym “HPHT” may be used interchangeably with the acronym “HTHP”. Both acronyms refer to the same thing, i.e. high pressure and high temperature, or high temperature and high pressure.
The current methods of forming TSP material cutting elements by HTHP sintering diamond particles adjacent a tungsten carbide substrate to form PCD bonded to the substrate and then removing the substrate and leaching the PCD to remove the catalyst is a relatively involved process which is relatively costly. Consequently any cutting element formed with such TSP material will also be costly. As such, methods of forming a TSP materials and method for forming cutting elements incorporating such TSP material which are more efficient and thus, less costly are desired.